Transient response of electric drives under utility upset conditions

This paper discusses the transient response of an electric drive system in a large pulp and paper distribution system which suffers occasional disturbances due to upsets in the utility system. Typical fault conditions such as line-to-ground fault and line-to-line fault in the utility transmission lines and distribution lines could severely depress mill power distribution voltages such that the normal operation of the AC or DC electric drive system could be adversely affected. Typical problems are fuse blowing inside the drive circuits when the drives operate in a regenerative mode. This paper identifies the problems by using computer simulations. Electromagnetic Transients Program (EMTP) is used to simulate the upset conditions. Detailed models of electric drives, motors, generators, transformers and distribution systems are included in the simulation. Furthermore, the paper provides some techniques and suggestions to improve the drive reliability, such as dead band and power electronics controller. Due to many varieties of drive central schemes, a general AC drive system with pulse-width-modulated (PWM) inverter is used for the study. However, the analysis and results are applicable to DC drive systems as well.